Linear variable differential transformer (LVDT) calibration mechanism for precision rigging with vibration and accuracy tracking robustness

ABSTRACT

Embodiments generally relate to assembly and methods for precisely rigging a linear variable differential transformer (LVDT). For example, the probe rod assembly of a dual tandem LVDT may comprise two moveable cores, a probe fitting, and a probe rod. Generally, the first moveable core may be configured to achieve electrical zero with its respective transformer. Without adjusting the position of the probe rod with respect to the one or more coils of wire, the second moveable core may be configured to achieve electrical zero with its respective transformer. This may ensure that both moveable cores simultaneously achieve electrical zero in the null position. Typically, the probe fitting may be configured to fit at a first end of the probe rod projecting outward from the outer housing. The disclosed assembly and methods may be used to precisely rig dual tandem LVDTs, single channel LVDTs, and dual parallel LVDTs.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

FIELD

The present disclosure relates to precision rigging of a linear variabledifferential transformer (LVDT).

BACKGROUND

In many industrial areas it may be necessary to measure movement and/orlinear displacement of externally coupled objects. Typically, a linearvariable differential transformer (LVDT) (also called linear variabledisplacement transformer) may be used to produce an electrical signalproportional to the displacement of a moveable core/slug (armature)within a transformer. LVDTs may often be utilized in the gaging andmeasuring arts to produce an electrical signal denoting location, size,or dimension. For example, LVDTs may be used within the aerospaceindustry to control the pitch on the blades of a helicopter tocompensate for winds during flight. LVDTs may be used inside an actuatorto accurately measure the movement and position of various elements usedin stabilization.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the following brief description, taken in connection withthe accompanying drawings and detailed description, wherein likereference numerals represent like parts.

FIG. 1A illustrates a cross-sectional view of an exemplary embodiment ofa dual tandem linear variable differential transformer (LVDT) comprisinga probe rod assembly located within a housing comprising one or morecoils of wire;

FIG. 1B illustrates a perspective view of an exemplary embodiment of adual tandem LVDT probe rod assembly (similar to the exemplary probe rodassembly shown in FIG. 1A);

FIG. 1C illustrates a schematic view of an exemplary embodiment of adual tandem LVDT probe rod assembly (similar to the exemplary probe rodassembly shown in FIG. 1A and FIG. 1B);

FIG. 2A illustrates a cross-sectional view of an exemplary embodiment ofa dual parallel LVDT comprising a probe rod assembly located within ahousing comprising one or more coils of wire;

FIG. 2B illustrates a schematic view of an exemplary embodiment of adual parallel LVDT probe rod assembly (similar to the exemplary proberod assembly shown in FIG. 2A);

FIG. 3A illustrates a cross-sectional view of an exemplary embodiment ofa single channel LVDT comprising a probe rod assembly located within ahousing comprising one or more coils of wire;

FIG. 3B illustrates a schematic view of an exemplary embodiment of asingle channel LVDT probe rod assembly (similar to the exemplary proberod assembly shown in FIG. 3A);

FIG. 4A illustrates a flowchart of an exemplary method of calibrating adual tandem LVDT; and

FIG. 4B illustrates a simplified flowchart of an exemplary method ofperforming calibration (similar to the exemplary flowchart of FIG. 4A).

DETAILED DESCRIPTION

It should be understood at the outset that although illustrativeimplementations of one or more embodiments are illustrated below, thedisclosed systems and methods may be implemented using any number oftechniques, whether currently known or not yet in existence. Thedisclosure should in no way be limited to the illustrativeimplementations, drawings, and techniques illustrated below, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

The following brief definition of terms shall apply throughout theapplication:

The term “comprising” means including but not limited to, and should beinterpreted in the manner it is typically used in the patent context;

The phrases “in one embodiment,” “according to one embodiment,” and thelike generally mean that the particular feature, structure, orcharacteristic following the phrase may be included in at least oneembodiment of the present invention, and may be included in more thanone embodiment of the present invention (importantly, such phrases donot necessarily refer to the same embodiment);

If the specification describes something as “exemplary” or an “example,”it should be understood that refers to a non-exclusive example;

The terms “about” or “approximately” or the like, when used with anumber, may mean that specific number, or alternatively, a range inproximity to the specific number, as understood by persons of skill inthe art field (for example, +/−10%); and

If the specification states a component or feature “may,” “can,”“could,” “should,” “would,” “preferably,” “possibly,” “typically,”“optionally,” “for example,” “often,” or “might” (or other suchlanguage) be included or have a characteristic, that particularcomponent or feature is not required to be included or to have thecharacteristic. Such component or feature may be optionally included insome embodiments, or it may be excluded.

The embodiments of this disclosure typically relate to a linear variabledifferential transformer (LVDT) to measure movement and/or lineardisplacement of externally coupled objects. Typically, a linear variabledifferential transformer (LVDT) (also called linear variabledisplacement transformer) may be used to produce an electrical signalproportional to the displacement of a moveable core/slug (armature)within a transformer. The transformer may comprise a central, primarycoil winding and two secondary coil windings on opposite ends of theprimary coil winding. In some embodiments, the primary coil winding andthe secondary coil windings may be oriented in a different configurationbut, typically, may accomplish the same purpose. Generally, the coilwindings may be coaxial. Typically, the moveable core/slug may bepositioned within the coil assembly. The moveable core/slug may providea path for magnetic flux linking the primary coil to the secondarycoils.

Typically, when the primary coil is energized with an alternatingcurrent, a cylindrical flux field may be produced over the length of themoveable core/slug. This flux field may produce a voltage in each of thetwo secondary coils that may vary as a function of the moveablecore/slug position. Generally, moveable core/slug position may move theflux field into one secondary winding and out of the other secondarywinding causing an increase in the voltage induced in one secondarywinding and a corresponding voltage decrease in the other secondarywinding. In some embodiments, the secondary coil windings may beconnected in series with opposing phase. Thus, the net output of theLVDT may be the difference between the two secondary voltages.Generally, when the moveable core/slug is positioned symmetricallyrelative to the two secondary windings (at the “null” position), thedifferential output may be approximately zero, because the voltage ofeach secondary coil winding is equal but of opposite phase.

LVDTs may often be utilized in the gaging and measuring arts to producean electrical signal denoting location, size, or dimension. For example,LVDTs may be used within the aerospace industry to control the pitch onthe blades of a helicopter to compensate for winds during flight. Insome embodiments, the LVDT may be used in actuators in flight controlstabilization actuation, for fuel control in aerospace engine valves,active control clearance for pneumatic or hydraulic valves, valves oractuators used in auxiliary power units, door closures, starter airvalve controls, variable stator vane actuators, variable bleed valveactuators, transient bleed valve actuators, thrust reversing actuators,brake actuators, landing gear actuators, flap/skew actuators,spoiler/aileron actuators, trim actuators, control of flight services,landing gear locks, level sensing, torque generators, and manifold valveactuation. LVDTs may be used inside an actuator to accurately measurethe movement and position of various elements used in stabilization.Generally, within an actuator, as the pressure increases, the moveablecore/slug may move toward one secondary winding and away from the othersecondary winding. This may yield a voltage difference that may beproportional to the linear movement. Thus, the voltage output maymeasure pressure and position.

Therefore, to ensure accurate measurement of position, LVDTs may need tobe precisely rigged to set the null position. Precision rigging of theLVDT assembly may decrease tracking, accuracy, and rigging error of theLVDT during use. Generally, due to constant movement of the elements ofthe LVDT during stabilization and the fact that a LVDT requires complexelectrical measurement to achieve accurate displacement measurement,there may be concerns for thermal stability, precision rigging, androbustness to vibration for the materials/elements used in the LVDTassembly. Conventionally, precise rigging of an LVDT may be accomplishedusing various set length components to form the probe assembly of theLVDT. Typically, with various set length components, adjustment of theprobe assembly may be limited (e.g. mobility of moveable/slug core maybe restricted) and the process of setting the LVDT to its null positionmay require finding the electrical zero before setting the rig position.Additionally, conventional methods may cause difficulty in settingtracking between multi-channel devices because each channel may need tobe set individually to compound tracking, accuracy, and rigging error.Additionally, with the use of various set length components, the LVDTsrobustness to vibration may rely on factors such as fastening methods,component design, process selection, and designed assembly for the probeassembly of the LVDT. With a greater number of factors affecting theLVDTs robustness to vibration, there may be a decreased confidence inthe LVDT performing accurately. Thus, generally, to offset the riggingerror, manufacturers may rely on tolerance stack. In some conventionalembodiments, LVDT probe assembly may rely on variable length components(e.g. shimming or maintaining precision component lengths) toaccommodate for component differences in order to set rig position orset tracking between channels. However, this method may not offerimproved vibration performance.

Disclosed embodiments relate to an LVDT precisely rigged to allow thenull position and tracking between one or more channels of the LVDT tobe set exactly at the electrical zero of the transformer. Typically,precision rigging may include redundant retention methods to lead torobust vibration. Additionally, a probe rod with an optimized outerdiameter may be implemented to improve precision rigging. Typically, aprobe rod with a large outer diameter may lead to cyclic failures (dueto a relative inflexibility). Typically, a probe rod with a small outerdiameter may cause the probe rod to bend and, potentially, break. Thus,it may be important to optimize the outer diameter of the probe rod asmay be accomplished by the disclosed embodiments.

For example, in some embodiments, the position of the moveable core/slugon the probe rod may be carefully selected to control the direction ofshift during use and to improve tracking between one or more channels ofthe LVDT assembly. In some embodiments, the LVDT probe rod assembly maybe calibrated and precisely rigged using the following exemplary method.First, the first channel's magnetic core/slug may be welded, brazed,threaded, or crimped at a fixed position on the probe rod through theuse of a protective spacer. The first channel's magnetic core/slug maybe precisely dialed to its electrical zero with its respectivetransformer by using a modified thread between the probe fitting and thefirst channel's magnetic core/slug at the adjacent end of the probe rod.Typically, the second channel's magnetic core/slug may then be preciselyset to its respective transformer's electrical zero through the use ofanother protective spacer with modified mating threads on the spacer(located at the opposite end of the probe rod from the probe fitting).This method of attaching/fastening the one or more moveable cores/slugsto the probe rod may allow for adjustment and retention as needed wherethe LVDT assembly may achieve a precisely configured null position.Typically, once the adjustments may be complete, the probe rod assemblymay be permanently fastened to achieve zero null coincidence, preciserig position, robust vibration performance, and superior temperaturetracking operation.

In some embodiments, the probe rod assembly may be configured for usewithin a dual tandem LVDT design, a dual parallel LVDT design, and/or asingle channel LVDT design. Generally, precision rigging of the LVDTprobe may vary depending on the type of LVDT design. However, typically,the LVDT calibration process may comprise similar steps regardless ofthe type of LVDT design. The steps of the calibration process may beperformed in the order described; however, the calibration process maybe performed in numerous other manners (e.g. in a different sequentialorder). Persons of skill should appreciate other methods of preciselyrigging an LVDT probe rode assembly to achieve zero null coincidence,robust vibration, and superior temperature tracking.

In some embodiments, during calibration and assembly of the LVDT proberod, the LVDT housing comprising the one or more coils may be pairedwith a probe rod. Typically, the part number (P/N) may berecorded/stored to ensure proper precision rigging of the probe rodtakes place within a corresponding LVDT housing to form the LVDT. Thisprocess may ensure that slight deviations in the method of manufacturingthe LVDT housing are accounted for while performing the calibrationprocess (e.g. setting null position, ensuring null concurrents, etc.).Deviations between various LVDT housings may take place due tovariations in the coil windings located within the housing. Persons ofskill should appreciate other such deviations that may result from notproperly pairing the LVDT housing and the LVDT probe rod during thecalibration and assembly process. In some embodiments, the deviations(between similarly manufactured LVDT elements) may be considerednegligible and pairing of the LVDT housing to the LVDT probe rodeassembly may not be required.

Generally, a dual tandem LVDT design may comprise two moveablecores/slugs attached to a probe rod. Typically, a dual tandem LVDT maycomprise two LVDTs combined within a single transducer such that theremay be two output signals. Typically, dual tandem LVDTs may be morereliable because failure in both output signals is highly improbable. Adual tandem LVDT may increase redundancy of the LVDT proving especiallyuseful for applications involving aircraft and missile control systems.To implement both LVDTs into one probe rod assembly may be a complextask. Generally, each moveable core/slug may need to be aligned with itscorresponding, respective channel such that both moveable cores/slugsachieve electrical zero. In some embodiments, the first channel'smoveable core/slug may be precisely dialed to its electrical zero withits respective transformer. Generally, this may be accomplished by usinga modified thread between the probe fitting and the first channel'smoveable core/slug. Typically, the first channel's moveable core/slugmay be permanently attached with reference dimensions towards the centerof the probe rod. Once the first channel's moveable core/slug achievesits electrical zero, the probe fitting may be permanently attached tothe probe rod. The second channel's moveable core/slug may be adjustedusing a protective spacer with optional mating threads on the spacer(located at the opposite end of the probe rod from the probe fitting).

In some embodiments, the probe rod assembly may be assembled in adifferent order. For example, the first channel's moveable core/slug maybe aligned to achieve its electrical zero, and then the second channel'smoveable core/slug may be aligned on the probe rod to achieve itselectrical zero while maintaining the first channel's moveablecore's/slug's electrical zero. The probe fitting may be aligned last.Typically, the manner by which the two moveable cores/slugs may bealigned may vary and, yet, accomplish the same purpose. Generally,either the first channel's moveable core/slug or the second channel'smoveable core/slug may be used as the reference by which to align theother corresponding elements. During calibration, the second channel'smoveable core/slug may be limited in motion by the presence of a currentclamp at one end of the probe rod.

In some embodiments, the one or more moveable cores/slugs and the probefitting may be temporarily attached to the probe rod during thecalibration process. Typically, temporary attachment may comprise usingone or more spacers attached to each end of the moveable core/slug.Additionally, the probe fitting may be temporarily attached to the proberod by using a modified thread (e.g. by screwing the probe fitting ontothe probe rod). In some embodiments, to improve robustness to vibration,the one or more moveable cores/slugs and the probe fitting may bepermanently attached to the probe rod during the calibration processand/or after the calibration process is complete. Typically, permanentattachment may comprise welding (e.g. friction welding), brazing,threading, or crimping the one or more moveable cores/slugs and/or theprobe fitting onto the probe rod. In some embodiments, an adhesive suchas epoxy may be used for permanent attachment of the one or moremoveable cores/slugs and/or the probe fitting. In some embodiments,multiple methods of permanent attachment may be used. In thisdisclosure, “permanently” and/or “permanent” attachment means that itmay be possible to use force to detach the one or moveable cores/slugsand/or the probe fitting from the probe rod. However, this method ofremoval may effectively damage the probe rod assembly. In other words,“permanently” and/or “permanent” attachment means that it would be veryinconvenient to remove the one or more moveable cores/slugs and/or theprobe fitting and may require the User and/or Manufacturer to dispose ofthe probe rod assembly in the instance removal or reorientation of theone or more moveable cores/slugs and/or the probe fitting is required.Thus, typically, permanent attachment of the one or more moveablecores/slugs and/or the probe fitting may take place after calibration(and, optionally, the accuracy test) is complete.

Generally, either both sides of the moveable core/slug or one side ofthe moveable core/slug may be permanently attached to the probe rod.Typically, permanent attachment of both sides of the moveable core/slugmay potentially lead to imbalance of the probe rod assembly.Additionally, permanent attachment of both sides of the moveablecore/slug may lead to problems arising due to temperature variation. Forexample, due to a temperature increase, the moveable core/slug may notbe able to expand and contract freely which may lead to the inability toachieve zero null coincidence. Typically, permanent attachment of oneside of the moveable core/slug may be seen as more favorable. This maybe because the moveable core/slug may be purposefully end balanced.Additionally, with only one side of the moveable core/slug requiringpermanent attachment, the error of wrongfully attaching the moveablecore/slug to the probe rod may be reduced. In other words, the chancesof error are reduced in half since only one side may require permanentattachment rather than both sides requiring permanent attachment.Additionally, the moveable core/slug may expand and contract freely withthe probe rod assembly as the temperature increases or decreases. Insome embodiments, the coefficient of thermal expansion (CTE) for theprobe rod and the moveable core/slug may be the same to allow forequivalent changes (e.g. lengthening, shortening, etc.) arising fromtemperature variation. While persons of skill should understand thedisclosed embodiments based on the above disclosure, the followingfigures may provide specific examples that may further clarify thedisclosure.

Turning now to the drawings, FIG. 1A illustrates a cross-sectional viewof an exemplary embodiment of a dual tandem linear variable differentialtransformer (LVDT) 100 comprising a probe rod assembly 110 locatedwithin a housing 120 comprising one or more coils 121. Typically, a dualtandem LVDT 100 may comprise two LVDTs combined within a singletransducer such that there may be two output signals 130 a, 130b.Typically, dual tandem LVDTs 100 may be more reliable because failure inboth output signals 130 a, 130 b is highly improbable. In the exemplaryembodiment of FIG. 1A, the dual tandem LVDT 100 comprises a housing 120having a longitudinal bore within which the probe rod assembly 110 maybe configured to move axially with respect to the housing 120.Typically, the probe rod assembly 110 of a dual tandem LVDT 100 maycomprise a probe fitting 115 and two moveable cores/slugs 112, 113. Asshown in the embodiment of FIG. 1A, one end of the probe rod 111 may fitwithin the longitudinal bore of the housing 120 and the other end of theprobe rod 111 (comprising the probe fitting 115) may extend outward fromthe longitudinal bore of the housing 120. Additionally, a dual tandemLVDT 100 may comprise two channels 140, 150. The first channel 140(located closer to the probe fitting 115) may comprise the firstmoveable core/slug 112 and the second channel 150 (located closer to theopposite end of the probe rod 111 away from the probe fitting 115) maycomprise the second moveable core/slug 113. Generally, each moveablecore/slug 112, 113 may need to be aligned with its corresponding,respective channel 140, 150 such that both moveable cores/slugs 112, 113achieve electrical zero.

FIG. 1B illustrates a perspective view of an exemplary embodiment of adual tandem LVDT probe rod assembly 110 (similar to the exemplary proberod 110 assembly shown in FIG. 1A). Generally, the probe fitting 115 andthe two moveable cores/slugs 112, 113 may be configured to slide and/orscrew onto the probe rod 111. Generally, each moveable core/slug 112,113 may comprise a spacer 114 attached to both ends of the moveablecore/slug 112, 113. In some embodiments, as in the exemplary embodimentof FIG. 1B, the moveable core/slug 113 of the second channel maycomprise an adjustment spacer 117. Typically, the adjustment spacer 117may be longer/larger to allow the second moveable core/slug 113 agreater extent of movement. Additionally, the adjustment spacer 117 maycomprise threaded ends such that it may be tightened or loosenedaccordingly. In some embodiments, the ratio of the rod 111 diameter tothe moveable core/slug 112, 113 diameter may be optimized to increasevibration and accuracy tracking robustness.

FIG. 1C illustrates a schematic view of an exemplary embodiment of adual tandem LVDT probe rod assembly 110 (similar to the exemplary proberod assembly 110 shown in FIG. 1A and FIG. 1B). During assembly,generally, each moveable core/slug 112, 113 may need to be aligned withits corresponding, respective channel such that both moveablecores/slugs 112, 113 achieve electrical zero. Thus, in the exemplaryembodiment of FIG. 1C, the moveable core/slug 112, 113 may be preciselydialed to its respective transformer's electrical zero. Typically, thismay be accomplished by using the modified thread 116 between the probefitting 115 and the first channel's moveable core/slug 112. Typically,the first channel's moveable core/slug 112 may be permanently attachedwith reference dimensions towards the center of the probe rod 111. Inthe exemplary embodiment of FIG. 1C, the first channel's moveablecore/slug 112 may be permanently attached to the probe rod 111 usingfriction welding. In some embodiments, the moveable core/slug 112, 113may be welded on both sides or only on one side. Once the firstchannel's moveable core/slug 112 achieves its electrical zero (e.g. bysliding the probe rod 111 within the housing until the transformerindicates electrical zero has been achieved), the probe fitting 115 maybe permanently attached to the probe rod 111. In the exemplaryembodiment of FIG. 1C, the probe fitting 115 comprises threading 116 toallow it to screw onto the probe rod 111. In some embodiments, the probefitting 115 may further be welded onto the probe rod 111 to increaserobustness to vibration. The second channel's moveable core/slug 113 maybe adjusted using a protective spacer 114 with optional mating threadson the adjustment spacer 117 (located at the opposite end of the proberod 111 from the probe fitting 115) (similar to the attachment of thefirst channel's moveable core/slug 112). Typically, this may allow thesecond channel's moveable core/slug 113 to remain affixed to the proberod 111. Generally, the second channel's moveable core/slug 113 may bealigned with its respective transformer to achieve electrical zero afteralignment of the first channel's moveable core/slug 112 and the probefitting 115 is complete. Generally, after calibration of the probe rodassembly 110 is complete (and, optionally, the probe rod assembly 110passes an accuracy test), all elements of the probe rod assembly 110 maybe welded. Typical areas of permanent attachment (e.g. welding) areindicated in the exemplary embodiment of FIG. 1C by the presence ofspacers 114, 117. However, not all areas indicated may comprisepermanent attachment. For example, only one side of both moveablecores/slugs 112, 113 may be permanently attached to the probe rod 111rather than both sides being permanently attached to the probe rod 111.

FIG. 2A illustrates a cross-sectional view of an exemplary embodiment ofa dual parallel LVDT 200 comprising two probe rods 211 located within ahousing 220 comprising one or more coils 221. Typically, a dual parallelLVDT 200 may comprise two output signals which may be useful in case offailure in one of the probe rods 211. Generally, each probe rod 211 maybe permanently attached to a shared probe fitting 215. In the exemplaryembodiment of FIG. 2A, the probe rods 211 are shown to be screwed (viathreads 216) into the probe fitting 215. However, in some embodiments,the probe rods 211 may be permanently attached to the probe fitting 215using methods such as frictional welding. Additionally, in the exemplaryembodiment of FIG. 2A, each probe rod 211 comprises a moveable core/slug212, 213. Typically, the moveable core/slug 212, 213 may be calibratedwithin the housing 220 to ensure that zero null coincidence is achieved.In some cases, each moveable core/slug 212, 213 may be calibratedindividually (for example, one moveable core/slug 212 may be calibratedwithin its channel and then the other moveable core/slug 213 may becalibrated within its respective channel). Generally, each moveablecore/slug 212, 213 may comprise a spacer 214 attached on either end. Thespacer 214 may serve to hold the moveable core/slug 212, 213 in place(e.g. frictional support) during the calibration process. In someembodiments, once calibration is complete, the spacers 214 on each sideof the moveable core/slug 212, 213 may be permanently attached (e.g.welded) to the respective probe rod 211. Typically, in the case ofwelding, the spacer 214 may comprise a material compatible to be laserwelded to the probe rod 211.

FIG. 2B illustrates a schematic view of an exemplary embodiment of adual parallel LVDT probe rod assembly 210 (similar to the exemplaryprobe rod assembly shown in FIG. 2A). Generally, each probe rod 211 maybe attached to a shared probe fitting 215, and each probe rod 211 maycomprise a moveable core/slug 212, 213. Typically, the magneticcore/slug 212, 213 may be located near the end of the probe rod 211.However, the distance of the moveable core/slug 212, 213 from the end ofthe probe rod 211 may be more specifically determined during thecalibration process. Typically, during the calibration process, theprobe rod assembly 210 may be loaded into a test stand. The voltage foreach channel may be measured, and if the measured voltage is less than aparticular threshold, then the moveable core/slug 212, 213 may bepermanently attached to its respective probe rod 211 (as discussed inreference to FIG. 2A).

FIG. 3A illustrates a cross-sectional view of an exemplary embodiment ofa single channel LVDT 300 comprising a probe rod assembly 310 locatedwithin a housing 320 comprising one or more coils 321. Generally, thesingle channel LVDT 300 may comprise a similar calibration process ascompared to the dual parallel LVDT 200. However, since a single channelLVDT 300 comprises a single probe rod 310 with a moveable core/slug 312,only one channel 340 may require calibration. Additionally, the singlechannel LVDT 300 may provide only one output signal. Generally, themethod of permanent attachment and attachment of the probe fitting 315to the probe rod 311 may be similar to the method described in referenceto FIG. 1A-FIG. 2B.

FIG. 3B illustrates a schematic view of an exemplary embodiment of asingle channel LVDT probe rod assembly 310 (similar to the exemplaryprobe rod assembly 310 shown in FIG. 3A). Typically, the moveablecore/slug 312 may be attached near one end of the probe rod 311 whilethe probe fitting 315 may be attached (e.g. screwed via threads 316) tothe other end of the probe rod 311. The probe fitting 315 comprisethreads 316 to allow removable attachment of the probe rod 311.Additionally, the probe fitting 315 may be permanently attached (e.g.welded) to the probe rod 311. Attachment of the moveable core/slug 312to the probe rod 311 may vary depending on whether or not calibrationhas been completed. Generally, during the calibration process, one ormore spacers 314 may be attached to either end of the moveable core/slug312. Typically, the spacers 314 may serve as frictional support of themoveable core/slug 312 to the probe rod 311 such that the moveablecore/slug 312 may not move freely. In other words, the spacers 314 maysnugly hold the moveable core/slug 312 onto the probe rod 311.Additionally, once calibration is complete, the one or more spacers 314may be permanently attached to the probe rod 311. Typically, the spacer314 may comprise a material compatible with the material of the proberod 311 such that laser welding may take place.

FIG. 4A illustrates a flowchart of an exemplary method of performingcalibration for a dual tandem LVDT. Generally, the calibration processmay take place within a test unit having a housing with one or morecoils of wire. Typically, the housing with the one or more coils of wiremay be associated with the particular probe rod assembly to ensureproper precision rigging of each LVDT. Thus, the Operator of the testunit may store the part number of the probe rod assembly to match withthe housing within which the test may take place. Once this is complete,the probe rod may be loaded into the test unit and moved until thecurrent clamp is met. The test unit table position may be set as zeroand moved into the load position. In the load position, the part (e.g.first moveable core, second moveable core, probe fitting, etc.) beingcalibrated and the spring may be loaded onto the probe rod. The testunit table may be moved to the zero position, and the Operator may readthe output signals from both Channel A and Channel B. If the differencebetween the output signals from Channel A and Channel B is less than anacceptable threshold level (e.g. 0.0005, 0.001, 0.005, etc.), then theOperator may check to determine if the average of the output signalsfrom Channel A and Channel B is less than the acceptable deviation fromelectrical zero (e.g. 0.0003, 0.001, 0.0002, 0.0015, etc.). If thedifference between the output signals between the two channels does notmeet the acceptable threshold level and/or the acceptable deviation fromelectrical zero, then the deviation from the acceptable threshold leveland/or the deviation from electrical zero may be calculated. TheOperator may then move the test unit table to load position androtate/slide the part undergoing calibration based on the calculateddeviations. Once the part may be adjusted, the Operator may move thetest unit table to the zero position and, once again, read the outputsignals to determine if the acceptable threshold level and theacceptable deviation from electrical zero is met. Generally, if both ofthese standards are met, the Operator may remove the probe rodcomprising the calibrated part from the test unit table and permanentlyfasten the calibrated part to the precise location on the probe rod.Typically, this procedure may be followed in part by the single channelLVDT and the dual parallel LVDT. In the case of the single channel LVDT,only one output signal may be transmitted. In this case, the Operatormay only tweak the location of the part being calibrated to ensure itdoes not exceed the acceptable deviation from electrical zero.Generally, this may be the case for a dual parallel LVDT. However, inthe case of a dual parallel LVDT, the Operator may need to check to seeif the acceptable deviation from electrical zero is being met by theparts (e.g. moveable core) within both channels. Generally, within asingle channel LVDT and a dual parallel LVDT, a difference between theoutput signals may not be determined. Thus, there may be no need todetermine if the acceptable threshold level for the difference is met.

FIG. 4B illustrates a simplified flowchart of an exemplary method ofperforming calibration (similar to the exemplary flowchart of FIG. 4A).Typically, the probe rod and/or additional parts (such as the firstmoveable core, the second moveable core, and probe fitting) may bemeasured to determine precise offset dimension. This may improveaccuracy during the calibration process since not all parts may beassembled/manufactured with precisely equal dimensions. Generally, thecalibration process may take place within a test unit having a housingwith one or more coils (similar to the process described in reference toFIG. 4A). The part may be loaded into the test unit/equipment and may beadjusted to precise rig position. Typically, the goal may be to achieveelectrical zero. Thus, the User/Operator may adjust the position of thepart until electrical zero is achieved. This process may include readingthe channel outputs of the part and comparing the output signal(s) todetermine whether or not the output signal(s) fit within a rig positiontolerance (e.g. within 0.0005, 0.001, 0.005, etc. from electrical zero).Typically, when the output signal(s) do not meet the rig positiontolerance, the deviation from rig position tolerance may be calculated,and the position of the part (e.g. first moveable core, second moveablecore, probe fitting) with respect to the respective transformer may beadjusted accordingly. Once the part(s) achieve output signal(s) meetingthe rig position tolerance, the part(s) may be coupled to the preciselocation.

In some embodiments, the calibration procedure may be followed up withan accuracy test. Typically, for the dual tandem LVDT, the accuracy testmay comprise gathering voltage data from both channels along the entirelength of the probe rod. Generally, by doing so, the Operator may beable to determine if the acceptable threshold and the acceptabledeviation from electrical zero is being met. Additionally, thisprocedure may potentially allow the Operator to implement signalconditioning circuitry to correct for potential errors that may arise,for example due to changes in temperature (e.g. if the deviation is toohigh, the signal conditioning circuitry may correct for the deviation).Typically, the accuracy test may be completed for the single channelLVDT and the dual parallel LVDT. As with the calibration test, theaccuracy test may check to see if the voltage being measured complieswith the acceptable deviation from electrical zero.

Having described device embodiments above, especially with regard to thefigures, various additional embodiments can include, but are not limitedto the following:

In a first embodiment, a (dual tandem) linear variable differentialtransformer (LVDT) comprising: an outer housing comprising one or morecoils of wire, wherein the one or more coils of wire are arranged toform a plurality of transformers, and wherein each transformer of theplurality of transformers defines a channel; a probe rod operable to fitwithin an opening in the outer housing (and operable to move withrespect to the outer housing); a first moveable core and a secondmoveable core coupled to the probe rod, wherein the second moveable coreis adjacent to an end spacer coupled to a first end of the probe rod;and a probe fitting coupled to a second end of the probe rod, whereinthe second end of the probe rod projects outward from the outer housing,wherein the first moveable core is coupled to the probe rod between thesecond moveable core and the probe fitting, and wherein the location ofthe second moveable core depends on the location of the probe fittingand the first moveable core. A second embodiment can include the LVDT ofthe first embodiment, wherein the LVDT comprises a first channel and asecond channel, wherein the first moveable core is configured to achieveelectrical zero with respect to the first channel, and wherein thesecond moveable core is configured to achieve electrical zero withrespect to the second channel. A third embodiment can include the LVDTof the first to second embodiments, further comprising one or morespacers, wherein the one or more spacers are configured to be disposedon the probe rod on either side of the first moveable core and thesecond moveable core. A fourth embodiment can include the LVDT of thefirst to third embodiments, wherein the probe fitting, the firstmoveable core, and the second moveable core are fixedly attached to theprobe rod. A fifth embodiment can include the LVDT of the first tofourth embodiments, wherein the fixed attachment comprises at least oneof: welding, brazing, crimping, adhesive, threading, or combinationsthereof. A sixth embodiment can include the LVDT of the first to fifthembodiments, wherein the one or more spacers comprise a materialcompatible for welding to the probe rod. A seventh embodiment caninclude the LVDT of the first to sixth embodiments, wherein the one ormore spacers comprise a friction element configured to form a frictionfit to hold the two moveable cores to the probe rod. An eighthembodiment can include the LVDT of the first to seventh embodiments,wherein the probe rod comprises a material with a coefficient of thermalexpansion (CTE) matched to a CTE of the outer housing. A ninthembodiment can include the LVDT of the first to eighth embodiments,wherein the first moveable core and the second moveable core comprise amaterial that has a relatively high magnetic permeability. A tenthembodiment can include the LVDT of the first to ninth embodiments,wherein at least one end of the first moveable core or the secondmoveable core is permanently attached to the probe rod. An eleventhembodiment can include the LVDT of the first to tenth embodiments,wherein the first moveable core and the second moveable coresimultaneously achieve electrical zero at a zero position of the LVDT. Atwelfth embodiment can include the LVDT of the first to eleventhembodiments, wherein the end spacer is one of the one or more spacersand is a threaded end spacer, wherein the threaded end spacer comprisesflats along half of the diameter to allow for adjustment along thelength of the probe rod. A thirteenth embodiment can include the LVDT ofthe first to twelfth embodiments, wherein the first moveable core andthe second moveable core are each coupled to the probe rod on a sameend. A fourteenth embodiment can include the LVDT of the first tothirteenth embodiments, wherein the one or more coils of wire withineach transformer are coupled to the outer housing and correspond to thecoupling between the first moveable core and the probe rod and thesecond moveable core and the probe rod. A fifteenth embodiment caninclude the LVDT of the first to fourteenth embodiments, wherein a(single channel) linear variable differential transformer (LVDT)comprises: an outer housing comprising one or more coils of wire,wherein the one or more coils of wire are arranged to form atransformer, and wherein the transformer defines a channel; a probe rodoperable to fit within an opening in the outer housing (and operable tomove with respect to the outer housing); a moveable core coupled to theprobe rod, wherein the moveable core is coupled adjacent to a first endof the probe rod; and a probe fitting coupled to a second end of theprobe rod, wherein the second end of the probe rod projects outward fromthe outer housing, wherein the location of the moveable core depends onthe location of the probe fitting. A sixteenth embodiment can includethe LVDT of the first to fifteenth embodiments, wherein a (dualparallel) linear variable differential transformer (LVDT) comprises: anouter housing comprising one or more coils of wire, wherein the one ormore coils of wire are arranged to form a first transformer within afirst channel of the outer housing and a second transformer within asecond channel of the outer housing; a first probe rod operable to fitthrough an opening in the outer housing and into the first channel ofthe outer housing; a second probe rod operable to fit through an openingin the outer housing and into the second channel of the outer housing,wherein the second channel of the outer housing is configured to layparallel to the first channel of the outer housing; a first moveablecore coupled to the first probe rod, wherein the first moveable core iscoupled adjacent to a first end of the first probe rod; a secondmoveable core coupled to the second probe rod, wherein the secondmoveable core is coupled adjacent to a first end of the second proberod; and a probe fitting coupled to a second end of the first probe rodand to a second end of the second probe rod, wherein the probe fittingprojects outward from the outer housing, and wherein the location of theprobe fitting relative to the first probe rod and the second probe roddepends on the positioning of the first moveable core and the secondmoveable core on each respective probe rod.

Exemplary embodiments might also relate to a method for calibrating aLVDT (e.g. similar to those described above, which may be consideredoptionally incorporated herein with respect to the discussion of thesystem). Such method embodiments, for example, might include, but arenot limited to, the following:

In a seventeenth embodiment, a method for calibrating a linear variabledifferential transformer (LVDT), the method comprising: fixedly couplinga first moveable core onto a probe rod; inserting the probe rod with thefirst moveable core into a housing comprising one or more coils of wire,wherein the one or more coils of wire are arranged to form a pluralityof transformers; aligning a position of the first moveable core withrespect to a first transformer of the plurality of transformers;adjusting a position of a probe fitting on the probe rod with respect tothe aligning of the position of the first moveable core to the firsttransformer of the plurality of transformers; fixedly coupling the probefitting to the probe rod; adjusting a second moveable core on the proberod; aligning a position of the second moveable core with respect to asecond transformer of the plurality of transformers based on thealigning of the position of the first moveable core to the firsttransformer; and fixedly coupling the second moveable core to the proberod after aligning the second moveable core relative to the secondtransformer. An eighteenth embodiment can include the method of theseventeenth embodiment, wherein the LVDT comprises a dual tandem LVDT. Anineteenth embodiment can include the method of the seventeenth toeighteenth embodiments, wherein fixedly coupling the first moveablecore, the second moveable core, and the probe fitting to the probe rodcomprises at least one of: welding, brazing, crimping, adhesive,threading, or combinations thereof. A twentieth embodiment can includethe method of the seventeenth to nineteenth embodiments, wherein atleast one end of the first moveable core and the second moveable core ispermanently attached to the probe rod. A twenty-first embodiment caninclude the method of the seventeenth to twentieth embodiments, whereininserting the probe rod into the housing comprises moving the probe rodinto the housing until a current clamp is met. A twenty-secondembodiment can include the method of the seventeenth to twenty-firstembodiments, wherein alignment of the first moveable core within thefirst transformer and alignment of the second moveable core within thesecond transformer comprises sliding the first moveable core and thesecond moveable core until electrical zero (e.g. null position) isachieved with respect to the first transformer and the secondtransformer, respectively. A twenty-third embodiment can include themethod of the seventeenth to twenty-second embodiments, wherein at azero position (e.g. null position/electrical zero achieved by the firstmoveable core and the second moveable core), the difference between theoutput signal of the first transformer and the output signal of thesecond transformer is less than an acceptable threshold level. Atwenty-fourth embodiment can include the method of the seventeenth totwenty-third embodiments, wherein when the difference between the outputsignal of the first transformer and the output signal of the secondtransformer is greater than the acceptable threshold level, thedeviation from the acceptable threshold level is calculated, and theposition of the first moveable core, the second moveable core, or theprobe fitting is adjusted accordingly. A twenty-fifth embodiment caninclude the method of the seventeenth to twenty-fourth embodiments,wherein the average of the output signal from the first transformer andthe average of the output signal from the second transformer is lessthan an acceptable deviation from electrical zero. A twenty-sixthembodiment can include the method of the seventeenth to twenty-fifthembodiments, wherein when the output signal from the first transformerand the output signal from the second transformer is greater than theacceptable deviation from electrical zero, the position of the firstmoveable core, the second moveable core, or the probe fitting isadjusted on the probe rod accordingly. A twenty-seventh embodiment caninclude the method of the seventeenth to twenty-sixth embodiments,further comprising one or more spacers, wherein the one or more spacersare configured to be disposed on the probe rod on either side of thefirst moveable core and the second moveable core. A twenty-eighthembodiment can include the method of the seventeenth to twenty-seventhembodiments, wherein one of the one or more spacers is a threaded endspacer, wherein the threaded end spacer is located at the opposite endof the probe rod from the probe fitting, and wherein the threaded endspacer comprises flats along half of the diameter to allow foradjustment along the length of the probe rod. A twenty-ninth embodimentscan include the method of the seventeenth to twenty-eighth embodiments,wherein calibrating a single channel LVDT comprises: fixedly coupling amoveable core onto a probe rod, inserting the probe rod with a moveablecore into a housing comprising one or more coils of wire, wherein theone or more coils of wire are arranged to form a transformer; aligning aposition of the moveable core with respect to the transformer; andadjusting a position of a probe fitting on the probe rod with respect tothe aligning of the position of the moveable core with respect to thetransformer. A thirtieth embodiment can include the method of theseventeenth to twenty-ninth embodiments, wherein calibrating a dualparallel LVDT comprises: fixedly coupling a first moveable core onto afirst probe rod; inserting the first probe rod with the first moveablecore into a first channel of an outer housing comprising one or morecoils of wire, wherein the one or more coils of wire are arranged toform a first transformer; aligning a position of the first moveable corewith respect to the first transformer; adjusting a position of the firstprobe rod with respect to a probe fitting, wherein adjusting theposition is based on the alignment of the position of the first moveablecore with respect to the first transformer; fixedly coupling a secondmoveable core onto a second probe rod; inserting the second probe rodwith the second moveable core into a second channel of the outer housingcomprising one or more coils of wire, wherein the one or more coils ofwire are arranged to form a second transformer, and wherein the secondchannel is configured to lay parallel to the first channel; aligning aposition of the second moveable core with respect to the secondtransformer; and adjusting a position of the second probe rod withrespect to the probe fitting, wherein adjusting the position is based onthe alignment of the position of the second moveable core with respectto the second transformer.

While various embodiments in accordance with the principles disclosedherein have been shown and described above, modifications thereof may bemade by one skilled in the art without departing from the spirit and theteachings of the disclosure. The embodiments described herein arerepresentative only and are not intended to be limiting. Manyvariations, combinations, and modifications are possible and are withinthe scope of the disclosure. Alternative embodiments that result fromcombining, integrating, and/or omitting features of the embodiment(s)are also within the scope of the disclosure. Accordingly, the scope ofprotection is not limited by the description set out above, but isdefined by the claims which follow, that scope including all equivalentsof the subject matter of the claims. Each and every claim isincorporated as further disclosure into the specification, and theclaims are embodiment(s) of the present invention(s). Furthermore, anyadvantages and features described above may relate to specificembodiments, but shall not limit the application of such issued claimsto processes and structures accomplishing any or all of the aboveadvantages or having any or all of the above features.

Additionally, the section headings used herein are provided forconsistency with the suggestions under 37 C.F.R. 1.77 or to otherwiseprovide organizational cues. These headings shall not limit orcharacterize the invention(s) set out in any claims that may issue fromthis disclosure. Specifically and by way of example, although theheadings might refer to a “Field,” the claims should not be limited bythe language chosen under this heading to describe the so-called field.Further, a description of a technology in the “Background” is not to beconstrued as an admission that certain technology is prior art to anyinvention(s) in this disclosure. Neither is the “Summary” to beconsidered as a limiting characterization of the invention(s) set forthin issued claims. Furthermore, any reference in this disclosure to“invention” in the singular should not be used to argue that there isonly a single point of novelty in this disclosure. Multiple inventionsmay be set forth according to the limitations of the multiple claimsissuing from this disclosure, and such claims accordingly define theinvention(s), and their equivalents, that are protected thereby. In allinstances, the scope of the claims shall be considered on their ownmerits in light of this disclosure, but should not be constrained by theheadings set forth herein.

Use of broader terms such as “comprises,” “includes,” and “having”should be understood to provide support for narrower terms such as“consisting of,” “consisting essentially of,” and “comprisedsubstantially of.” Use of the terms “optionally,” “may,” “might,”“possibly,” and the like with respect to any element of an embodimentmeans that the element is not required, or alternatively, the element isrequired, both alternatives being within the scope of the embodiment(s).Also, references to examples are merely provided for illustrativepurposes, and are not intended to be exclusive.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another system,or certain features may be omitted or not implemented.

Also, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as directly coupled or communicating witheach other may be indirectly coupled or communicating through someinterface, device, or intermediate component, whether electrically,mechanically, or otherwise. Other examples of changes, substitutions,and alterations are ascertainable by one skilled in the art and could bemade without departing from the spirit and scope disclosed herein.

What is claimed is:
 1. A linear variable differential transformer (LVDT)comprising: an outer housing comprising one or more coils of wire,wherein the one or more coils of wire are arranged to form a pluralityof transformers, and wherein each transformer of the plurality oftransformers defines a channel; a probe rod operable to fit within anopening in the outer housing and operable to move with respect to theouter housing; a first moveable core and a second moveable core coupledto the probe rod, wherein the second moveable core is adjacent to an endspacer coupled to a first end of the probe rod; and a probe fittingcoupled to a second end of the probe rod, wherein the second end of theprobe rod projects outward from the outer housing, wherein the firstmoveable core is coupled to the probe rod between the second moveablecore and the probe fitting, and wherein the location of the secondmoveable core depends on the location of the probe fitting and the firstmoveable core.
 2. The LVDT of claim 1, wherein the LVDT comprises afirst channel and a second channel, wherein the first moveable core isconfigured to achieve electrical zero with respect to the first channel,and wherein the second moveable core is configured to achieve electricalzero with respect to the second channel.
 3. The LVDT of claim 1, furthercomprising one or more spacers, wherein the one or more spacers areconfigured to be disposed on the probe rod on either side of the firstmoveable core and the second moveable core.
 4. The LVDT of claim 3,wherein the one or more spacers comprise a material compatible forwelding to the probe rod, and wherein the one or more spacers comprise afriction element configured to form a friction fit to hold the twomoveable cores to the probe rod.
 5. The LVDT of claim 1, wherein theprobe fitting, the first moveable core, and the second moveable core arefixedly attached to the probe rod.
 6. The LVDT of claim 5, wherein thefixed attachment comprises at least one of: welding, brazing, crimping,adhesive, threading, or combinations thereof.
 7. The LVDT of claim 1,wherein the probe rod comprises a material with a coefficient of thermalexpansion (CTE) matched to a CTE of the outer housing.
 8. The LVDT ofclaim 1, wherein at least one end of the first moveable core or thesecond moveable core is permanently attached to the probe rod.